# CVE-2026-20831: Microsoft Windows Ancillary Function Driver privilege escalation

Source: https://junglewise.ai/threats/cve-2026-20831-microsoft-windows-ancillary-function-driver-privilege-escalation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-01-13. Updated: 2026-07-30  
License: CC BY 4.0 with a link back

CVE-2026-20831 · Severity: high · CVSS 7.8 · Published 2026-01-13

A security vulnerability exists in a core Windows networking component that handles socket connections. An attacker who already has basic access to a computer could exploit this flaw to gain full administrative control over the system. This could allow them to install programs, view or delete sensitive data, or create new accounts with full user rights.

Technologies: [Microsoft Windows 11](https://junglewise.ai/threats/technologies/windows-11), [Microsoft Windows Server 2008 R2](https://junglewise.ai/threats/technologies/windows-server-2008-r2), [Microsoft Windows 10](https://junglewise.ai/threats/technologies/windows-10). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft).

## Quick answers

**Is CVE-2026-20831 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-20831 being exploited in the wild.

**How severe is CVE-2026-20831?** High severity, with a CVSS score of 7.8, published 13 January 2026.

**Which products and versions are affected?** Microsoft Windows 11 22H3, 23H2, 24H2, 25H2; Microsoft Windows Server 2008 R2 All versions; Microsoft Windows 10 1607, 1809, 21H2, 22H2.

**Is there a fix for CVE-2026-20831?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-20831 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-20831?** Check whether you run Microsoft Windows 11, Microsoft Windows Server 2008 R2 or Microsoft Windows 10 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

This vulnerability is a Time-of-Check Time-of-Use (TOCTOU) race condition (CWE-367) located within the Windows Ancillary Function Driver (afd.sys), which serves as the entry point for the Windows Sockets (WinSock) API. An attacker with low-privileged local access can exploit this race condition by timing a change to a shared resource between the moment the driver validates a condition and the moment it uses the resource. Successful exploitation allows the attacker to execute code with SYSTEM privileges. The vulnerability affects a wide range of Windows client and server versions, and Microsoft has released security updates to address the issue.

## Affected products

- Microsoft Windows 10 1607, 1809, 21H2, 22H2
- Microsoft Windows 11 22H3, 23H2, 24H2, 25H2
- Microsoft Windows Server 2008 R2 Service Pack 1 All versions

## Timeline

- 2026-01-13: disclosed
- 2026-01-13: advisory

## References

- [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20831](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20831)

## Related threats

- [Microsoft Windows Recovery Environment UEFI/BIOS password bypass](https://junglewise.ai/threats/cve-2026-116638-the-windows-recovery-environment-winre-in-windows-10-and-11-may)
- [Use after free in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally.](https://junglewise.ai/threats/cve-2026-68820-microsoft-windows-ancillary-function-driver-for-winsock-use-after)
- [Microsoft Windows Backup Engine privilege escalation](https://junglewise.ai/threats/cve-2026-58598-microsoft-windows-backup-engine-privilege-escalation)
- [Microsoft Windows Boot Loader security feature bypass](https://junglewise.ai/threats/cve-2026-58638-microsoft-windows-boot-loader-security-feature-bypass)
- [Microsoft Windows Client-Side Caching Service privilege escalation](https://junglewise.ai/threats/cve-2026-58637-microsoft-windows-client-side-caching-service-privilege)